Individualized Rehabilitation for Osgood-Schlatter or Sever Pain in Youth Athletes

The goal of this clinical trial is to learn if a 12-week individualized rehabilitation program is feasible and helpful for children and adolescents with lower-extremity apophyseal pain, including Osgood-Schlatter-related knee pain and Sever-related heel pain. It will also learn about how well participants follow the program, whether the program can be delivered as planned, and whether pain, function, and sports participation improve during rehabilitation. The main questions it aims to answer are: 1. Can this rehabilitation program be delivered with good attendance, good home-exercise adherence, and complete follow-up data? 2. Do pain, function, and sports participation improve during the rehabilitation period? 3. Which baseline clinical, functional, ultrasound, maturity, or biomarker features may help explain who responds better to rehabilitation? All participants will receive the same overall rehabilitation framework. The program includes education, pain and load monitoring, an activity-ladder approach, symptom-guided exercise progression, motor-control training, basic strength exercises, and gradual return to running, jumping, landing, and sport-specific activities. Exercises are individualized according to symptoms, current activity level, movement quality, treatment tolerance, and clinical judgement. Participants will: 1. Attend baseline and follow-up physiotherapy assessments. 2. Receive an individualized rehabilitation plan with education, pain and load monitoring, and home exercises. 3. Complete home exercises and keep a short symptom and activity log. 4. Attend in-person physiotherapy review visits during the rehabilitation period. 5. Answer questionnaires about pain, function, perceived change, and sports participation during follow-up.

Inclusion Criteria: * Aged 10 to 17 years * Participates in organized sport and has at least 12 months of sport participation or training history * Has current lower-extremity apophyseal pain consistent with Osgood-Schlatter-related knee pain and/or Sever-related heel pain, or has previous Osgood-Schlatter-related or Sever-related symptoms with a residual or low-irritability presentation relevant to rehabilitation * Meets criteria for at least one pre-specified rehabilitation entry pathway: post-trial rehabilitation entry after completion of the separate photobiomodulation trial, or direct-entry rehabilitation with active apophyseal symptoms, or direct-entry rehabilitation with previous Osgood-Schlatter-related or Sever-related symptoms and a low-irritability or residual presentation For participants entering with active symptoms: * pain is located at the tibial tubercle region and/or the calcaneal apophyseal/heel region * pain is aggravated by activity, loading, or sport participation * pain is reproducible on clinical examination or the clinical history is consistent with the target condition Participant and parent/caregiver are willing to take part in the rehabilitation program, including in-person visits, home exercises, symptom/activity monitoring, and follow-up assessments. A parent or legal guardian provides written informed consent, and the participant provides assent when applicable. Exclusion Criteria: * Current pain episode started after an acute traumatic injury that better explains the symptoms * Clinical presentation suggests a condition other than the target rehabilitation condition, including a major alternative knee or heel diagnosis requiring different management * Lower-limb surgery that would substantially affect rehabilitation planning, safety, or interpretation of outcomes * Known serious musculoskeletal, neurological, rheumatological, inflammatory, autoimmune, metabolic, or other systemic disease that may affect safe participation or interpretation of outcomes * Any medical or developmental condition that would prevent safe participation in exercise-based rehabilitation * Current symptoms requiring urgent medical assessment or management outside the rehabilitation pathway * Inability to understand study instructions or complete study procedures with parent/caregiver support * Parent/caregiver or participant does not agree to participate or withdraws consent/assent